Autism Spectrum Disorder (ASD) is a group of developmental disorders which affects approximately 1% of children, a prevalence rate that is increasing annually. The molecular basis of ASD is likely to be complex and heterogeneous, but given the central role of the inhibitory neurotransmitter GABA in cognitive control, development and plasticity and a growing body of evidence linking GABAergic dysfunction to autism and autistic phenotypes, the GABA system is a strong potential area for ASD research. Recently, it has become possible to measure GABA concentration non-invasively in the brain using magnetic resonance spectroscopy (MRS), and in an extremely novel set of experiments we have shown that differences in regional GABA concentration among healthy subjects have measurable behavioral correlates. For example, GABA concentration in sensorimotor cortex correlates with performance at a somatosensory discrimination task (see below); this may have particular relevance for autism, as atypical response to tactile stimuli is a common (and diagnostic) feature of autism and one that can substantially impair behavioral function This proposal arises from a collaboration between Dr Richard Edden (PI) and Dr Stewart Mostofsky (Co-I) to apply the extremely novel pairing of MRS of GABA with somatosensory paradigms to investigate whether there is a measurable GABA deficit in autism, and whether this correlates with autism associated differences in somatosensory processing. The findings from examination of GABA MRS and its association with autistic behavior will provide a foundation for investigating novel treatment therapies, specifically use of medications that increase GABAergic activity. In Aim 1, we will compare measurements of GABA concentration in a group of 20 children with ASD between the age of 8 and 12 years with 20 age-, gender-, and IQ-matched typically developing children (TDC) as the control group. In Aim 2, we will perform psychophysical measures of tactile discrimination to investigate whether there are differences between children with ASD and TDC, and in Aim 3 we will test whether the abnormal tactile processing commonly observed in ASD arises from a GABAergic deficit.